The invention relates to a cathode ray tube comprising an in-line electron gun including means for generating electron beams and electrodes.
Such cathode ray tubes are known and are employed, inter alia, in television receivers and computer monitors.
In such a cathode ray tube, three electron beams are generated in the in-line electron gun, which electron beams extend in one plane, the in-line plane. These electron beams are deflected across a display screen in two mutually perpendicular directions by means of a deflection means. A color selection electrode, for example a shadow mask, is arranged between the electron gun and the display screen.
A factor which is of great importance for the quality of the image displayed is the accuracy with which the three electron beams converge. Convergence errors adversely affect the picture quality.
An external magnetic field (for example the terrestrial field) influences the electron beams and hence may cause convergence errors and adversely affect the picture quality.